As communities prepare for crowded July Fourth celebrations, cities and towns across the country have revived juvenile curfews and increased police patrols in response to an apparent uptick in large teen gatherings and fights organized through social media.

Communities in states including California, Florida, Maryland, North Carolina, South Carolina and Virginia have announced or expanded curfews for minors this year, while others have tightened enforcement in downtown entertainment districts, parks and shopping centers where officials say “teen takeovers” have become more common.

In Laurel, Maryland, a summer curfew took effect in June as part of what Mayor Keith R. Sydnor described as a broader effort to keep young people safe while encouraging them to take part in recreation programs and community events.

“This curfew is one part of a broader effort to keep our youth safe, strengthen families, and ensure our community remains a safe and welcoming place for everyone,” Sydnor said in a news release.

Washington, D.C., has taken an even tougher approach. Federal officials recently warned that parents could face prosecution if their children repeatedly violate the city’s curfew, part of a broader crackdown on youth violence and disorder in popular commercial areas.

Research on youth curfews has generally found little evidence that they significantly reduce crime or victimization. Critics also argue the policies can lead to unnecessary interactions between police and young people who are not committing crimes, which may disproportionately affect children of color.

The renewed focus on curfews comes as cities brace for one of the busiest weekends of the summer. Along with Independence Day celebrations, many communities are hosting events tied to the nation’s 250th birthday, prompting additional security measures and larger police presence in public gathering spaces.

But not every city is relying on enforcement alone.

After a downtown “teen takeover” that resulted in 22 arrests in May, city officials in Tampa, Florida, launched a free weekend “Stay & Play” program, opening recreation centers on Friday, Saturday and Sunday nights with sports, games, free meals and mentoring for teens.

Baltimore has similarly expanded late-night recreation programming during the summer months, keeping select community centers open during evening hours to give young people supervised places to gather.

City leaders say those programs complement curfews by providing alternatives rather than simply telling teenagers where they cannot go.

Some youth advocates say that approach addresses a broader challenge. As shopping malls continue to decline, recreation centers often close early and many activities require money or transportation, teenagers have fewer free places to gather with friends. Large meetups in parks, downtowns and shopping districts may fill that void, but some of those gatherings have devolved into fights, vandalism or other disturbances.

In response, some cities and private property owners have also turned to “no unaccompanied minors” policies in malls and commercial areas. Some youth advocates say those rules can have the unintended effect of punishing all young people for the behavior of a few, further limiting the already shrinking number of public spaces where teens can safely spend time outside of school or home.